The present invention relates to an apparatus for molding a recorded disc and particularly to such an apparatus which includes an internally heated center plate for securing a stamper to the mold plate.
An apparatus suitable for molding recorded discs and particularly high density recorded discs, such as capacitive electronic discs (CED), is described in copending applications for U.S. Letters Patent of Michael Lee McNeely, Ser. No. 093,012, filed Nov. 9, 1979, entitled Apparatus for Producing Disc Records Having Molded-in Center Holes, and Robert Winfield Chambers et al, Ser. No. 187,161, filed Sept. 15, 1980, entitled Apparatus for Molding a Recording Disc, which are incorporated herein by rererence. In general, the apparatus of each of these applications includes a pair of opposed mold plates having recesses in their opposed surfaces. At least one of the mold plates is movable toward the other to bring the recesses together to form a mold cavity of the desired shape and size for the recorded disc. On the opposed surfaces of the mold plates are stampers. Each stamper is a thin metal plate having a central hole therethrough and a surface relief pattern on one surface which is the negative of the pattern to be formed in the recorded disc. The outer edge of each stamper is secured to its respective mold plate by a hold down ring. The center hole in each stamper is in alignment with a center hole in its respective mold plate and a center plate fits into the aligned holes and secures the inner edge of the stamper to the mold plate. A center hole forming pin is slidably mounted in a passage in the center plate in the upper mold plate. The bottom center plate has a raised central portion which mates with the bottom of the center hole forming pin to form a center hole in the molded recorded disc.
During the molding of a disc, the mold plates and stampers are first heated by passing steam through passages in the mold plates. The center hole forming pin is likewise heated by passing steam through a passage in the pin. Later in the molding cycle the mold plates, stampers and center hole forming pin are cooled by passing water through the respective passages. In order to achieve a uniform heating across the entire mold cavity, it has been found desirable to also heat the center plate of the bottom mold plate. Attempts have been made to attach a heater to the end of the bottom center plate, but this has not been satisfactory because it heats the center plate by conduction, which is too slow. Therefore, it would be desirable to have a center plate which is directly heated, such as by a flow of steam therethrough. However, because of the manner of securing the bottom center plate in the bottom mold plate, it is difficult to connect steam inlet and outlet pipes to the end of the center plate to achieve the direct heating of the center plate.